Axial flow compressors with circular arc blades



April 15', 1958 E. A. ST ALKER 2,830,753

AXIAL FLow CQMPRESSORS WITH CIRCULAR ARC BLADES Original Filed Nov. 10,1951 mp v INVEN TOR nited States AXIAL FLOW COgggESSORS WITH CIRCULARBLADES Edward A. Stalker, Bay City, Mich.

7 Claims. (Cl. 230-120) This invention relates to axial flow compressorsand particularly to structures therefor which are economical to produce.

An object of this invention is to provide novel aerodynamic structuresfor compressors which can be produced by simple machine tool operations.

Another object is to provide cases and blades of simple shape whichcooperate to provide efficient flows of fluid therebetween. I t

Other objects will appear from the description drawingsand claims. r l

This application is a division of my U. S. application Serial No.255,799, filed November 10, 1951, entitled Axial Flow Compressors, nowabandoned.

The above objects are accomplished by the means illustrated in theaccompanying drawings in which- Figure 1 is a fragmentary development ofthe blades of a prior art compressor rotor which have airfoil crosssections;

Figure 2 is a fragmentary development of the rotor blades of acompressor according tothe subject invention;

Figure 3 shows graphs of the variation in the cross sectional areas ofrotor passages expressed as a ratio to the cross sectional area of thepassage at the inlet thereto;

Figure 4 is a fragmentary axial section through a compressor accordingto the subject invention;

Figure 5 is an alternate blade section defining the location of themaximum mean camber height above the subtending chord C;

Figure 6 is a fragmentary development of the stator blades of thecompressor of Fig. 4;

Figure 7 shows an alternate-blade section;

Figure 7a shows a fragmentary perspective view of a rotor incorporatingblades similar to that of Fig. 7; and

Figure 8 shows still another blade section.

This division of the parent application is directed to lower circulararcs extending substantially to the leading and trailing edges, and tosuch blades whose spanwise elements lie along radial lines extendingoutward from the rotor hub.

Figure l shows a fragmentary development of the blades ofa rotor stageof a prior art axial flow compressor. The blades are of airfoil sectionand it will be observed that the-streamlines 10 and 12 of the fluid flowof a relative fiuid flow first converge in passing through the passages13 between the blades 14 and then later diverge.

The convergence indicates an increasing velocity along substantiallengths of the forward parts of the blades which keep their boundarylayers in a laminar state. Then for the forward portion of each blade,the resistance or drag loss is low since as is well known, a laminarflow of the boundary'layer has less loss than a turbulent flow.

The main aerodynamic advantage of an airfoil section for a compressorblade resides inthe production of i Patented Apr. 15, 1958 theaccelerated flow along the forward portion of the blade and'not in someoverall characterization of airfoils.

The fabrication of blades of airfoil shape is very costly because of theconstantly varying radii of curvature chordwise along the bladeincluding varying nose radii along the blade span.

Sheet metal blades are readily stamped or pressed to shape and becausethe thickness is constant a simple tool operation, such as performed bya shaper tool for instance, can provide the nose radius desired.

Sheet metal blades of constant thickness (with rounded leading edges andsharpened trailing edges) are cheap to produce but they do not providesignificant acceleration of the flow for a significant distance inpassing along the forward portions of the blades. In Fig. 2 thestreamlines, contiguous with the boundaries or contours of the bladesections of the blades 24, are 20 and 22 and it will be observed thatthere is no significant acceleration of the flow along a significantlength of blade chord.

The cross sectional width and areas are measured along such lines as 21and 23 normal to the flow lines on the contours of the blades. Theblades are said to be peripherally curved when their sections are curvedin peripheral surfaces about the rotor axis.

The aerodynamic advantages of the blades with airfoil section and theeconomic advantages of the sheet metal blades are combined by thepresent invention. This is accomplished as shown in Figs. 2-4 for oneembodiment of the invention by varying the shape of the bounding walls,namely case 30 and hub 32 so that the flow passages 36 between bladeseach decreases in cross sectional area for a substantial chordwisedistance. The

portion of each passage rearward of the portion of decreasing crosssectional areas has increasing cross sectional areas rearward therealongbecause of the peripheral or chordwise curvature in the blades.

In Fig. 3, curve 34 shows the variation in cross sectional area of eachrotor passage 36 along the axial length L for blades of constantthickness as made from a sheet. A, is the cross sectional area at anypoint along the passage and A is the cross sectional area at the inletto a rotor passage between adjacent blades. Curve 40 is for an alternatepassage wherein the throat occurs aft of the mid length of the passageand is particularly suited to high velocity of the flow relative to theblade. Both curves, 34 and 40, disclose a greater cross sectional exitthan inlet area indicated by the ratio of A; and A; greater than 1. V

In Fig. 4 the rotor 32 is rotatably supported by the shaft 44 andbearings 46 and 48. The blades 24 are peripherally spaced about the hub32 at the pitch angle 6 measured with respect to the direction of theaxis of rotation 53. The rotor is' contained in the case 30 and issucceeded by the stator 56 comprising the blades 58 and inner case orwall 60.

The case 36} and rotor hub 32 converge toward each other at the rotorposition to provide acceleration of the flow along the forward portionsof the sheet blades 24 according to-curve 34 of Fig. 3. Thus eachpassage has a converging portion providing a throat of smaller crosssectional area than the inlet cross sectional area.

The throat is succeeded downstream by cross sectional areas ofprogressively increasing magnitude with the exit cross sectional areagreater than the inlet cross sectional area. The increase in crosssectional area along the aft portion of a rotor passage is provided bythe curving of the blades along their chords to place said aft portionsmore nearly parallel to the axis of rotation. Thus cross section 23 isgreater than cross section 21. Consequently the case and hub surfacesmay be approximately parallel along the aft portions of the rotorpassages.

The shapes required of the case and the hub are produced by turning ason a lathe and are therefore cheap to make. Thus the combination. of lowcost sheet blades and turned case and hub provides a very economicalstructure which is aerodynamically efficient.

The sheet blades may also take the form 24 shown in Fig. where thedistance X to the maximum ordinate 55 of the mean camber line 61 may beaft of the mid point of the chord C. Fig. 5 shows it in the neighborhoodof the 80% point of the chord. Such blades are preferably used with thecross sectional areas varying in the manner shown by curve 40 in Fig. 3.

The stator 56 as shown in Fig. 4 and Fig. 6 has sheet blades 58 similarto the rotor blades. The cases 30 and 60 constitute respectivelyradially inner and outer walls bounding the stator passages. These wallsconverge in the downstream axial direction along the forward portion 62of each stator passage 64 between blades so that the cross sectionalareas decrease along this portion. Along the aft portion of each statorpassage the blades are curved in the peripheral direction so that thecross sectional areas increase with the exit cross sectional areagreater than the inlet cross sectional area.

Another form of the invention is shown in Figs. 4, 7 and 7a wherein theupper contour of each blade section is a circular are extending fromsubstantially the trailing edge to substantially the leading edge andthe lower contour is also a circular are extending in like manner.

Sheet blades are the most economical to produce but other economicalblade forms may also be combined with the passage shape to give passageflows of low drag loss. For instance, the blade may have circular arcs71 and 72, Fig. 7, forming its crescent shaped blade section 73. Theleading edge has a constant nose radius along the blade span so that itis readily cut as by a shaper or miller tool. Such blades can beproduced economically. The case and hub can be given such contours thatthe desired acceleration of the flow will take place along the forwardportions of the blades. Fig. 7a shows a fragmentary perspective view ofthe rotor in Fig. 4 wherein blades 73 of Fig. 7 have been substituted.

The circular arc blade presents a thicker blade which insomeapplications will resist vibrations in a superior manner.

The blading is preferably arranged so that there is no significantdiffusion of the flow along a portion of each passage close to its exit.This is done by making the aft portions of the mean camber lines ofblades substantially parallel or by tapering the case or hub so that thecross sectional area of each passage is substantially constant for ashort distance just ahead of the trailing edges. Curves 34 and 40 ofFig. 3 show a short length of no diffusion. This should be from 5% to25% of the axial length of the blades with a preferred value of 10%.

If there is no diffusion of the flow just before reaching the trailingedges of the blades, the rotor is not applying a force to the air and sothere will be no difference in pressure between opposite sides of theblade. If a difference of pressure existed there would be a vortex format each blade trailing edge with a consequent loss. By eliminating thediffusion just forward of the trailing edge a substantial improvement inefficiency is obtained.

The greater the maximum mean camber ordinate and the further rearward itis located, the more important it is that the diffusion be terminatedahead of the trailing edges. In particular the diffusion should beterminated well ahead of the trailing edge when the maximum mean camberordinate is not less than 5% of the blade chord and/or the position ofthe mean camber maximum ordinate is aft of the midpoint of the bladechord.

The blades of this invention are particularly suited to compressorrotors which give the fluid a rotation wherein all the peripheralvelocity is proportional to the radius. Such a rotation may be called arigid body type of rotation.

Bladed compressor rotors which are designed to give the fluid a wheel orrigid. body type of rotation can be designed to have the same Machnumber at all points along the blade span. Since the Mach number is thesame as the nose radius of the blade sections can be the same at allsections along the blade span.

The blade whose blade sections are composed of circular arcs can havegreater thickness at the root portion adjacent the hub than at the tipportion adjacent the case while retaining the constant nose radius alongthe span-by making the tip chord less than the root chord and the tipsection thickness ratio greater than the root section thickness ratioreferred to the respective chord lengths.

Circular arc blade sections, Figs. 7 and 8, provide some accelerationalong the forward halves and the amount of acceleration can be increasedbetween the leading edges and rearward points of the chords by taperingthe case or hub or both as described earlier herein.

Where a large range of mass flow is desired for a given rate ofrotation, the nose radius should be a large percentage of the chord ofthe blade section 79 as shown in Fig. 8. The upper and lower contours 81and 82 are circular arcs and the maximum thickness is well forward alongthe chord. This section in a cylindrical duct has a very short noseportion about equal to the radius bathed by an accelerated flow but bytapering the hub and case the flow can be made accelerating along even amajor portion of the chord length if desired such as'indicated by curve40 of Fig. 3.

Preferably the blades are arranged so that all elements of each bladelie along radial lines so that the centrifugal force on the elements donot move them significantly laterally. Thus the centrifugal force ischiefly resisted by tension stresses and the blade does not tend tountwist due to the centrifugal forces. This is substantiallyaccomplished by having the major portions of the blade over itschordwise and spanwise extents in coincidence with chordwise spacedradial lines from the axis of rotation passing through the root sectioninside its contours.

An axial flow compressor is characterized by having rotor flow passageswhich are directed in the general direction of the axis from an inlet atthe front of the rotor to an exit at the rear of the rotor, facingrearward to discharge fluid rearward relative to the rotor in thegeneral direction of the axis.

While I have illustrated specific forms of the invention, it is to beunderstood that variations may be made therein and that I intend toclaim my invention broadly as indicated by the appended claims.

I claim: 1. In combination in an axial flow compressor, a case, a

' hub rotatably mounted in said case defining an annular channeltherewith, and a plurality of blades on said hub having leading andtrailing edges extending radially and being spaced peripherallythereabout and dividing said annular channel into a plurality of .rotorflow passages defined between said leading and trailing edges of saidblades and bounded by said case and hub and having inlets and exits forflow of fluid therethrough respectively adjacent said leading andtrailing edges, said case and hub converging relative to each other inthe downstream direction along forward portions of said rotor passagesto progressively reduce the cross sectional areas thereof along saidforward portions, said forward portions being succeeded downstream byrearward portions of said rotor passages of progressively increasingcross sectional areas with the exit cross sectional areas of said rotorpassages larger than the inlet cross sectional areas thereof, each saidblade having spanwise spaced blade sections along a major portion ofsaid leading edge transverse thereto, each said section being defined bya contour comprising an upper circular arc and a lower circular arespaced apart at mid chord and extending with the same respective radiiof curvature over substantially the entire distance between the leadingand trailing edges, each said are extending continuously fromsubstantially said leading edge to substantially said trailing edge andconverging one relative to the other toward said edges.

2. In combination in an axial flow compressor, a blade structure mountedfor rotation about an axis comprising a plurality of peripherally spacedblades having their spans extending radially and defining a plurality offlow passages therebetween, each said blade having blade sectionstransverse to said span along a major portion thereof, each said sectionhaving a contour comprised of an upper circular arc and a lower circulararc spaced apart extending with the same respective radii of curvatureover substantially the entire distance between the leading and trailingedges and defining a maximum thickness at about the midpoint of thechord of said blade, and an outer wall and an inner wall bounding saidflow passages, said walls converging one relative to the other so thatthe forward portion of each said passage has decreasing cross sectionalareas rearward therealong, said blades being curved along the chordsthereof providing in cooperation with said walls increasing crosssectional areas for the rearward portions of said passages with the exitcross sectional area of each said passage greater than the inlet crosssectional area thereof.

3. In combination in an axial flow compressor, a blade structurecomprising a plurality of peripherally spaced blades having spans andleading and trailing edges extending radially and defining a pluralityof flow passages between said blades for conducting a flow of fluidrearward therethrough, each said passage having an inlet at the forwardend thereof and an exit at the rearward end thereof respectivelyadjacent said leading and trailing edges, each said blade havingspanwise spaced blade sections along a major portion of said spantransverse thereto, each said section being defined by a contourcomprised of an upper circular arc and a lower circular are providing alocality of maximum blade thickness along the blade chord, each said areextending chordwise with the same radius of curvature substantially tothe leading edges of said sections and to the trailing edges thereof,and an outer wall and an inner wall at radially opposite ends of saidblades bounding said flow passages, said walls converging one relativeto the other downstream along the forward portion .of each passagedecreasing the cross sectional areas rearward therealong to a point aftof said localities of said maximum thickness, said blades being curvedin the peripheral direction providing in cooperation with said wallsincreasing cross sectional areas downstream along the rear portions ofsaid passages, the cross sectional area of said exit of each saidpassage being larger than the cross sectional area of said inletthereof.

4. In combination in an axial flow compressor, a blade structure mountedfor rotation about an axis'comprising a plurality of peripherally spacedblades having spans extending radially and defining a plurality of flowpassages between said blades for conducting a flow of fluid rearwardtherethrough, each said blade having its blade sections comprised of anupper circular arc and a lower circular are spaced apart at mid chordand converging one relative to the other toward the ends thereof placingthe maximum thickness of said sections at about the midpoint of thechord, each said are extending chordwise with the same radius ofcurvature substantially to the leading edge of said sections and to thetrailing edge of said blade, and an outer wall and an inner wall atradially opposite ends of said blades bounding said flow passages, saidwalls converging one relative to the other asap-Jess N (i so that theforward portion of each passage has decreasing cross sectional areasrearward therealong, said blades being curved along the chords thereofproviding in cooperation with said walls increasing cross sectionalareas for the rear portions of said passages, the nose radii of saidblade sections being substantially constant along each blade span, theexit cross sectional area of each said passage being larger than theinlet cross sectional area thereof.

5. In combination in an axial flow compressor, a case, a hub mounted insaid case'for rotation about an axis defining an annular channeltherewith, and a plurality of axial flow blades carried on said hub andspaced peripherally thereabout with the leading and trailing edgesextending in the general radial direction and dividing said annularchannel into a plurality of rotor axial flow passages defined betweeninlets and exits thereof respectively adjacent said leading and trailingedges of said blades, each said blade having spanwise spaced bladesections including a root section adjacent said hub, each said sectionhaving a contour comprising an upper circular arc and a lower circularare spaced apart at mid chord and closely adjacent one to the other atsaid leading and trailing edges positioning the maximum thickness atabout mid chord of said section, each said arc extending with the sameradius of curvature continuously from substantially said leading edge tosubstantially said trailing edge, said blades being curved along thechords thereof providing in cooperation with said hub and said caseincreasing cross sectional areas for the rearward portions of saidpassages with the exit cross sectional area of each said passage greaterthan the inlet cross sectional area thereof to provide a pressure risein said rotor passages.

6. In combination in an axial flow compressor, a case, a hub mounted insaid case for rotation about an axis defining an annular channeltherewith for flow of fluid rearward therein, and a plurality of axialflow blades carried on said hub and spaced peripherally thereabout withthe leading and trailing edges extending in the general radial directionand with said blades dividing said annular channel into a plurality ofrotor axial flow passages defined between inlets and exits thereofrespectively adjacent said leading and trailing edges of said blades,each said blade having spanwise spaced blade sections including a rootsection, said sections extending transversely of said span at difierentangles relative one to another and to said axis defining a twist in saidblade, each said section having a contour comprising an upper circulararc and a lower circular are spaced apart at mid chord and closelyadjacent one to the other at said leading and trailing edges, each saidare extending with the same radius of curvature from substantially saidleading edge to substantially said trailing edge, said blades beingcurved along the chords thereof providing in cooperation with said huband case rearwardly increasing cross sectional areas for the rearwardportions of said passages with the cross sectional area of said exit ofeach said passage greater than the cross sectional area of said inletthereof to provide a pressure rise in said rotor passages, each saidblade over major portions of its chordwise and spanwise extents being incoincidence with chordwise spaced radial lines from said axis throughsaid root section inside the contour thereof to preclude centrifugalforces from altering said twist.

7. In combination in an axial flow compressor, a case, a hub mounted insaid case for rotation about an axis defining an annular channeltherewith, and a plurality of axial flow blades carried on said hub andspaced peripherally thereabout with the leading and trailing edgesextending in the general radial direction and dividing said annularchannel into a plurality of rotor axial flow passages defined betweeninlets and exits thereof respectively adjacent said leading and trailingedges of said blades, each said blade having spanwise spaced bladesections including a root section adjacent said hub, each saidsection'havinga contour comprising an upper circular arc and a lower"circular arc, each said are extending from substantially saidleadingedge to substantially said trailing edge, said case and said hubconverging relative to each.

other along forward portions of said rotor passages to reduce the crosssectionalareas thereof along said forward portions rearward from saidinlets, said blades being curved along the chords thereof providing-incooperation with said hub and said case increasing cross sectional areasfor rearward portions of said passages succeeding rearwardly saidforward portions thereof with the exit crosssectional area of each saidpassage greater than the inlet cross sectional area thereof to provide apressure rise' in each said" rotor passage.

References Cited in the file of this patent UNITED STATES PATENTS1,086,754' Curti Feb. 10, 1914 2,258,794 Way Oct. 14, 1941 2,258,795 NewOct. 14, 1941 2,628,768 Kantrowitz Feb. 17, 1953

